Please help, Mesa Mark IV "died" today

[surfingalien]

Basically, I need help trying to find out what went wrong. I've got a Mesa Mark IV small head that I use with a Boss GT-8 (effects loop/ 4 cable method). It is hooked up to a 2x12 rectifier cab (8ohms in). Today in practice the amp shut down, fan and everything. I did notice a smell of burning something, lasted about 2 min. or less, and that smell followed just a quick dying down of the guitar sound. This was the same time that the amp shut down and I noticed it b/c of the sound dying first, then looked at the amp and the lights/fan were off. Don't assume anything (besides that I know how to use the effects loop properly, always warm up/warm down my amp, always supply amp with a load). Also, some information that might help someone diagnose the problem:
1) set at pentode, simul class (all 4 power tubes), harmonics
2) all preamp tubes are new, power tubes have been used since September of 2005, but I play everyday. Related question: Can a tube dying cause the transistor (or whatever else) to die? And thus lead to the whole amp shutting down?
3) This amp is greater than 10 years old, which probably means the main power supply is messed up, but I'm not sure.

Please give me some insight as to what the cause of the problem likely was as well as what I need to do to fix it. Thanks!

 

[screamingdaisy]

Did you check the fuse? Sometimes a dying power tube will blow the fuse.

If the fuse is blown, pop a new one in and power it up while watching the power tubes. If one looks odd starts glowing bright red that's the bad tube. Shut down immediatly and replace that tube.

If the fust isn't blown, then take it to a tech.


On a side note, my amp did a similar thing awhile ago where the amp crackled then died and had the smell of burning electronics. It turned out to be the power switch had failed, so it was an easy fix, but I wouldn't recommend doing it yourself. Check the fuses and tubes, and if that doesn't fix it, take it to a tech.

 

[t0aj15]

Did you check the fuse? Sometimes a dying power tube will blow the fuse. If the fuse is blown, pop a new one in and power it up while watching the power tubes. If one looks odd starts glowing bright red that's the bad tube. Shut down immediatly and replace that tube. If the fust isn't blown, then take it to a tech.

I agree, sounds like a bad power tube to me. Do what daisy said.

 

[surfingalien]

Thanks a bunch, I will replace the fuse and check the tubes...

 

[guitargonaut]

If you bought the amp used, don't just check for blown fuses, but also check the value of the fuses. If you have a higher amp rating on a fuse you need to replace it with the right fuse. If you find a fuse with the wrong amp rating, the previous owner might have put it in there to cover up another problem. Something else in the circuit might have blown up instead of the fuse.

I hope this isn't the case, but it's something important to check for in a used amp.

Good luck!

 

[surfingalien]

Okay, thanks. Edit: 3 amp slo-blo fuse, which is correct, but the one in it is 250V, don't think the V matter though (Mesa recommends 100 or 117V).

 

[screamingdaisy]

Okay, thanks. Edit: 3 amp slo-blo fuse, which is correct, but the one in it is 250V, don't think the V matter though (Mesa recommends 100 or 117V).

Is the fuse still good, or is/was it blown?

 

[Tuna141]

You are correct. A 250V fuse is fine. As long as the fuse has a voltage rating equal to or greater than the line voltage it'll work fine.

 

[surfingalien]

Thanks for the replies, fuse was blown, and when I replaced it, everything started working again. I don't know why the fuse blew though. The tubes all look good to me, tested them for about half an hour at the same settings.

 

[Dasein]

How is it that you didn't think to check the fuse immediately? Just a brain-blip?

Also -- make sure you still don't have a tube issue because something caused your fuse to fail - be it age or some other issue with the amp, and you don't want to be in a situation where you blow a fuse again - especially at a gig or something. (I learned the hard way that showing up at a gig without spare tubes/fuses etc is not a good thing.)

R.

 

[surfingalien]

No, it wasn't a brainfart, more like a noobie question (which is why I came to this forum :roll: ). But yeah, I'll see if I can figure out what caused the fuse to blow. Any other ideas besides bad tubes that have been common with the older Mark IVs?

 

[RussB]

surfingalien,

Not to be rude, but you should download yourself a copy of the MKIV owner's manual and read through it. There are some great troubleshooting tips in there. You can find it at the Mesa website.

 

[surfingalien]

Thanks, it is pretty helpful.

 

[screengrid]

Hi,

I also want to say, that it is important to find out the real reason for the blown fuse. Please remember, you told us, that you noticed a smell of burning over a minute. Rarely smell is caused by a blown fuse itself.
For example, their are screnngrid resitors at the two outer power tubes ( Class A section ) which perhaps became too hot by a temporarely failure of the power tube. Those screengrid resistors typically like to blow / burn caused by a short of the power tube, also with a blown fuse at the same time


regards